FSX Won't Start Up

I got FSX the other day and have been playing happily. However, when I came to start it up just now it shows the FSX screen (to show it is loading) but it then crashes and I have to force quite it in the Task Manager. I have tried rebooting waiting 15 mins everything.
Anyone know why it is not starting despite working just a few hours earlier?
Is my only option to un-install and then re-insall?
Cheers
Tom
P.S. I AM using SP1
Anyone know why it is not starting despite working just a few hours earlier?
Is my only option to un-install and then re-insall?
Cheers
Tom
P.S. I AM using SP1